During its closest and most daring encounter with Saturn’s moon Enceladus, NASA’s Cassini spacecraft sampled an organic brew erupting from the surface in geyser-like fashion that resembles the composition of a comet.
Cassini’s dive through the watery plumes spewing from the so-called “tiger stripe” fissures took it between 50 and 190 kilometres from the surface, giving an unprecedented view of Enceladus’ icy terrain and a chance to sample directly the composition of the plumes. Cassini’s instruments measured an extremely high density of volatile gases, water vapour, carbon dioxide and carbon monoxide, as well as organic materials, some 20 times denser than expected.
"A completely unexpected surprise is that the chemistry of Enceladus, what's coming out from inside, resembles that of a comet," says Hunter Waite, principal investigator for the Cassini Ion and Neutral Mass Spectrometer instrument. "To have primordial material coming out from inside a Saturn moon raises many questions on the formation of the Saturn system."
"Enceladus is by no means a comet,” adds Waite. “Comets have tails and orbit the sun, and Enceladus' activity is powered by internal heat while comet activity is powered by sunlight. Enceladus' brew is like carbonated water with an essence of natural gas.”
Heat radiating from the entire length of 150 kilometre long fractures is shown in this heat map of the active south polar region of Enceladus. The yellow stars mark the source locations of the geysers, and correlate to the hottest parts of the fractures. Image: NASA/JPL/Space Science Institute.
New heat maps of the surface show higher temperatures than previously recorded in the south polar region. Hot tracks running the length of the giant tiger stripe fissures reach a balmy -93 degrees Celsius, compared with a background temperature of around -165 degrees Celsius measured at other nearby locations. The warmest parts of the fractures mark the points from which the geysers emanate, and implies that temperatures inside the moon may be even hotter, perhaps warm enough to allow water to be liquid.
"These spectacular new data will really help us understand what powers the geysers,” says John Spencer, Cassini scientist on the Composite Infrared Spectrometer team. “The surprisingly high temperatures make it more likely that there's liquid water not far below the surface."
The new results are allowing scientists to build up a comprehensive picture of the enigmatic satellite, and now that some of the main ingredients for life have been identified - organics, an energy source, and the potential for a reservoir of water below the icy shell - the astrobiological potential of Enceladus is looking more promising with every Cassini flyby.